Morita Shogi 64 checksum fixer

checksum.c

#include <stdio.h>

unsigned int checksum(unsigned char *data, int length) {
  unsigned char bVar1;
  unsigned int uVar2;
  int iVar3;
  
  uVar2 = 0xffff;
  bVar1 = *data;
  
  while(1) {
    data = data + 1;
    iVar3 = 0;
    uVar2 = (unsigned int)bVar1 << 8 ^ uVar2;

    do {
      if ((uVar2 & 0x8000) == 0) {
        uVar2 = uVar2 << 1;
      }
      else {
        uVar2 = uVar2 << 1 ^ 0x1021;
      }
      if ((uVar2 & 0x8000) == 0) {
        uVar2 = (uVar2 & 0xffff) << 1;
      }
      else {
        uVar2 = (uVar2 & 0xffff) << 1 ^ 0x1021;
      }
      if ((uVar2 & 0x8000) == 0) {
        uVar2 = (uVar2 & 0xffff) << 1;
      }
      else {
        uVar2 = (uVar2 & 0xffff) << 1 ^ 0x1021;
      }
      if ((uVar2 & 0x8000) == 0) {
        uVar2 = (uVar2 & 0xffff) << 1;
      }
      else {
        uVar2 = (uVar2 & 0xffff) << 1 ^ 0x1021;
      }
      uVar2 = uVar2 & 0xffff;
      iVar3 = iVar3 + 4;
    } while (iVar3 != 8);
    
    length -= 1;
    
    if (length == 0) break;
    
    bVar1 = *data;
  }

  return ~uVar2 & 0xffff;
}

int main(int argc, char **argv) {
  char save[0x200];

  if(argc < 2) return 1;

  printf("%s\n", argv[1]);

  FILE *f = fopen(argv[1], "rb");
  if(!f) return 1;

  if(fread(save, 0x100, 2, f) != 2) return 1;

  unsigned short c1 = checksum(save, 0xef);
  unsigned short c2 = checksum(save + 0x100, 0xef);

  printf("%04x\n%04x\n", c1, c2);

  fclose(f);

  return 0;
}